1. Field of the Invention
This invention relates to a recording medium, such as a video tape or a video disc, on which are recorded encoded moving picture signals. The present invention also relates to a picture display system for decoding and reproducing a recording medium having recorded thereon these encoded moving picture signals.
2. Description of the Related Art
FIG. 1 shows the structure of a conventional picture display system, that is an illustrative structure of an encoding/decoding system having an encoding unit 110 for encoding moving picture signals in general, and a decoding unit 130 for decoding the data encoded by the encoding unit 110.
To an input terminal 101 of the encoding unit 110 are supplied signals of a continuous picture (time-domain moving pictures). These input picture signals are first encoded by an encoder 102 and thence supplied as encoded data to a multiplexer 104.
The encoder 102 takes a frame-to-frame difference or executes discrete cosine transform (DCT) for eliminating redundant portions of the original pictures (input picture signals) on both the time axis and on the frequency axis, and encodes the resulting signal.
The encoder 102 executes the encoding in accordance with the so-called MPEG (Moving Picture Experts Group)-1/2 video standard, as an example of the encoding. Thus, a unit of the data sequentially outputted by the encoder 102 (encoded data), or unit data, corresponds to the signal of a sole original picture (one-frame or one-field signals) encoded in accordance with the MPEG standard, or a set of encoded moving picture signals under the MPEG standard, or a group-of-pictures (GOP). How the unit data is processed is determined depending on the capacity of a buffer memory, not shown, provided in a multiplexer 104 as later explained and on the data volume of the encoded data.
The encoder 102 also outputs the information specifying the data volume of the output encoded data and the other information which are sent to a control code generator 103.
The control code generator 103 generates various control codes pertinent to the encoded data, based on the encoded data, and sends the generated control codes to the multiplexer 104. If the encoder 102 is constructed in accordance with the MPEG standard, the control codes denote the information such as various headers and time stamps.
The multiplexer 104 multiplexes the encoded data from the encoder 102 and the control codes for the control code generator 103 to output the resulting multiplexed data. The multiplexer 104 also maintains continuity of the output data. That is, the upstream side encoder 102 eliminates the redundant portions of the input picture signal on both the time axis and the frequency axis, as described above, so that the input picture signal portion high in redundancy is compressed, while the input picture signal portion low in redundancy is not compressed sufficiently. The result is that continuity is not assured for the encoded data outputted by the encoder 102. Thus the multiplexer 104 causes the output encoded data of the encoder 102 to be temporarily stored in a buffer memory in order to output the data which becomes continuous data on read-out. Moreover, the multiplexer 104 is also configured for supplying to the encoder 102 the information on the residual volume of the buffer memory (total storage capacity less the stored volume of the encoded data), while the encoder 102 is configured for setting a parameter governing the volume of encoded data, such as the quantization step used for quantizing the data of the original picture) based on the information on the residual amount from the multiplexer 104. This prevents overflow or underflow of the multiplexer 104. For multiplexing, the standard of the MPEG system can be used.
The multiplexed data containing the output encoded data of the multiplexer 104, rendered continuous as described above, is outputted from an output terminal 105 of the encoding unit 110 for recording on the recording medium 120. The recorded data is subsequently reproduced and supplied to an input terminal 131 of the decoding unit 130.
In the decoding unit 130, multiplexed data inputted to the input terminal 131 is sent to a demultiplexer 132 which then separates the encoded data and various control data from the multiplexed data to send the encoded data and the control codes to a decoder 133 and to a control circuit 134, respectively.
The control circuit 134 controls the decider 133 based on the control codes supplied thereto. The decoder 133 decodes the encoded data, under control by the control circuit 134, to generate decoded picture signals. It is noted that the time point at which the encoded data is fed to the decider 133 is not coincident with the time point at which the encoded data is decoded by the decoder 133. Thus, for timing adjustment, the demultiplexer 132 temporarily stores the encoded data in a buffer memory, not shown, and reads out the stored encoded data responsive to the decoding state in the decoder 133 to transmit the read-out data to the decoder 133.
The decoded picture signal, obtained by decoding by the decoder 133, is outputted at an output terminal 135 of the decoding unit 130.
The decoded picture signals, outputted by the decoding unit 130, is subsequently supplied to, for example, a display unit, for display.
With the above-described conventional picture display system, a recording medium 120, purchased overseas, having recorded thereon picture signals, such as a motion picture, may be brought to Japan for decoding and reproduction by the decoding unit 130 marketed in Japan. The reverse case, of course, is possible.
From this it follows that a recording medium produced somewhere in the world based on the same standard can be decoded and reproduced by a decoding device produced somewhere based on the same standard.
Meanwhile, a copyright holder entertains the desire to delay or suspend sale of a recording medium for a specified territory, even although the recording medium is produced based on the same standard.
For example, there are occasions wherein a recording medium having recorded a motion picture thereon cannot be marketed or possessed in Japan owing to legal ban. However, it may occur that those who traveled abroad purchase such recording medium and carry it unknowingly into Japan. It is noted that the contents of the recordings can be confirmed on the overseas site of purchase on very rare occasions. In such case, the goods may be seized by the customs house to cause loss to the user.
Moreover, if a motion picture is being exhibited on the theater by road show, the promoter may entertain a desire to prohibit a recording medium having recorded thereon the motion picture already sold overseas from being brought to Japan in consideration of possible future profit resulting from the disclosure in Japan of the motion picture.
However, the recording medium, sold in overseas nations, and regularly purchased by a traveler, can hardly be legally prohibited from being moved to another territory or nation.